Epstein-Barr virus (EBV) is a gamma-herpesvirus that has infected the majority of the post-adolescent human population. EBV is the causative agent in infectious mononucleosis and is also associated with a number of tumors of lymphoid and epithelial origin, including B and T cell lymphomas and cancers of the upper throat. EBV infects both epithelial cells and B cells, requiring the fusion of viral and cellular membranes. The membrane fusion process needs four EBV proteins (gp42, gH, gL and gB) when B cells are targeted but only three for epithelial cells (gH, gL and gB). The gp42 protein controls the specificity of infection. EBV gp42 binds to a receptor to trigger entry into B cells, but gp42 inhibits membrane fusion with epithelial cells. The gp42 protein also binds tightly to the EBV gH/gL complex, interacting with gH/gL through its N-terminal region. The goal of this project is to develop a high throughput screening assay for the identification of inhibitors of EBV protein interactions, focusing on the gp42 interaction with gH/gL. This interaction is essential for virus- mediated membrane fusion and virus infection and small molecule inhibitors of the interaction will enable the development of antiviral therapeutics as well as provide new tools to dissect the mechanism of herpesvirus entry. Epstein-Barr virus (EBV) is associated with a number of human cancers, especially in individuals whose immune system is weakened because of disease or transplantation. Current work is focused on understanding the initial steps in virus infection, which require the merging of the viral envelope with that of the cell. The proposed research will allow for the identification of inhibitors of the virus entry into cells, potentially opening up new therapeutic routes to preventing EBV infection and transformation of susceptible human cells. [unreadable]